The nominal predicate and the S-P predicate construction are the natural corollary of the topic prominent feature of the Chinese language. The very definition of topic is given in terms of ‘pragmatic aboutness and relevance’; therefore, topic may not be grammatically or semantically related to comment or determined by comment (Lambrecht, 1994). Comment could be a verb phrase, a clause, or a nominal phrase; so long as it is contextually related to the topic and adds some information about the topic, the sentence is well-formed and meaningful. In the nominal predicate sentence, the predicate role is assumed by a NP, whose meaning can be construed as relevant to the first NP or the topic in the context. In the ‘S-P predicate’ case the comment is realized by a clause with its subject and predicate. Hence it is the ‘open and pragmatic relation’ between topic and comment that gives rise to the nominal predicate and S-P predicate constructions in Chinese.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.